Earnest Lawrence: Inventor of cyclotron

ERNEST O LAWRENCE In 1929 Lawrence began working on the suggestion of the astro-physicist A.S. Eddington (1882-1944) that nuclear reactions might occur at very high energies, as in the stars. The linear accelerator then available was not powerful enough for light ions. Lawrence evolved a scheme of acceleration in a spiral path.

Lawrence attended public schools in Canton and in Pierre, South Dakota (U.S). On completing high school in 1917, he attended Saint Olaf College, a small Lutheran College in Minnesota on a scholarship for a year and transferred to the University South Dakota where he became interested in physics. One of the teachers even then recognised the boy's unusual aptitude for science. He graduated with high honours (1922).

Then Lawrence enrolled at the University of Minnesota. He earned his M.S. under the direction of Professor Swann with a disseration on the experimental confirmation of ``the theory of induction in an ellipsoid rotation in a magnetic field''. Lawrence followed Swann to the University of Chicago where he came into contact with famous physicists of that period - A.A. Michelson, Arthur Compton and Niels Bohr.

In 1924 he again followed Swann to Yale University and completed his doctoral thesis (1928) on a study of the photoelectric effect in potassium vapour.

He gained quickly a reputation as a brilliant experimenter. In 1928 Lawrence moved to the University of California at Berkley and startled his colleagues by accepting a faculty position - exchanging a famous old university for a little-known state university.

Its subsequent world renown as a centre of research was due to the pre-eminence of its physics faculty, in par with Cambridge and Goettingen. Lawrence became a professor in 1930, at the young age of 29.

The resultant apparatus (named later the cyclotron) gave particles accelerations with energies high enough for nuclear reactions to take place.

Working of the cyclotron

This was in the shape of a flat circular can cut into two D- shaped halves with a high-frequency oscillator connected between.

The charged particles are introduced at the centre and the particles get deflected in a circular path by a magnetic field along the axis of the can.

The apparatus designed by Lawrence and his student Livingston acted rather like an electric motor with the armature replaced by the revolving stream of ions. With proper synchronisation, the oscillating field serves to impart successive accelerations to each particle, sending it on an ever-widening path with increasing velocity as it spirals outward.

When it approaches the wall, it can be deflected through an opening toward a target, which it hits with a high velocity, thereby producing nuclear disintegration.

A sufficiently strong magnet was not immediately available. Lawrence displayed his ingenuity by persuading the Federal Telegraph Company to donate an eighty-ton iron core which was no longer needed by the company.

With this magnet and a cyclotron chamber 27.5 inches in diameter, Lawrence was able to produce energies of millions of electron volts. Birth of high energy physics. This achievement ushered in the area of high-energy physics and made possible the disintegration of atomic nuclei, artificial isotopes and the discovery of new elements.

The disintegration of lithium was one of the first major results achieved in the Berkley cyclotron. Many heavier nuclei were disintegrated which was unique in 1932, the `annus mirabilis' year of modern physics.

These integrations proved that nearly every nuclear reaction takes place if there is sufficient energy for it, which led to the rapid development of nuclear physics They also enabled the accurate determination of the building energy of various nuclei, a verification of Einstein's famous equation relating energy and mass.

Lawrence and his younger brother John, a physician, explored medical uses for both neutrons and radio-isotopes form the cyclotron. Neutrons were used to destroy malignant tissues and were shown to be more effective than X-rays (1936).

It is Lawrence who launched the style of ``big-science'', creating large-scale physics laboratories at Berkley, and set the pattern around the world in organisations such as CERN, Geneva that were established later. He became the director of the Radiation Laboratory at Berkley.

This laboratory helped to devise a method of obtaining fissionable materials.

The electromagnetic separation method evolved at Berkley was later used in a large laboratory at Oak Ridge Tennessee, which provided the separated U-235 for the fission bombs dropped on Hiroshima and Nagasaki (1945).

Lawrence and Edward Teller sponsored a second laboratory at Livermore, for research on nuclear weapons.

Here larger and more efficient accelerators were designed and constructed while the Berkley laboratory was limited to research in basic science.

Plutonium and neptunium were isolated in this laboratory in 1940. Lawrence was actively involved in the subsequent controversy about the advisability of developing another, more powerful weapon, the hydrogen bomb. Oppenheimer (The Hindu, May 31, 2001) had deep disagreement with Lawrence on this issue, the final break came when the former, in a `cause celebre', lost the security clearance he needed as a project consultant.

Several honours followed in succession: Member of the National Academy of Sciences, Royal Society's Hughes Medal (1937), Nobel Prize in Physics (1939), element 103 named Lawrencium and a number of honorary degrees. Lawrence's name is commemorated in the two Radiation Laboratories, now known as the Lawrence Berkley Laboratory and the Lawrence Liver more Laboratory.

Annual Lawrence awards are given to young scientists. Lawrence participated, at the request of President Eisenhower, in the Conference of Experts in Geneva (1958) to study the suspension of nuclear tests.

Struck by recurrent colitis, he was flown home for an operation, which he did not survive (August 27, 1958).(The dictionary of scientific biography, New York) R.Parthasarathy

R. Parthasarathy

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